LEARNING AND RETENTION OF WARDS AND DESIGNS FOLLOWING EXCISION FROM MEDIAL OR LATERAL TEMPORAL-LOBE STRUCTURES

We sought to elucidate the contributions of the amygdala, hippocampus and temporal neocortex to learning and memory for verbal and visuospat ial material. Two matched learning tasks, using abstract words versus abstract designs, were administered to patients with unilateral neocor ticectomy (NCE; Dublin), selective amygdalohippocampectomy (AHE; Zuric h) of anterior temporal-lobe resection invading the amygdala and hippo campus (ATL; Montreal). Data were analysed according to side and type of resection. Learning and recall for words was impaired in groups wit h resection from the left temporal lobe, irrespective of whether medio basal structures were spared or temporal neocortex was spared. All rig ht-resection groups were unimpaired. Learning for abstract designs was impaired across all trials in the right AHE and NCE groups, and on th e last two trials in the right ATL group. Restricted deficits of lower magnitude were observed on some trials in left-resection groups. Thes e results show a partial dissociation between side of excision and typ e of material, but the finding of similar deficits in all resection ty pes was unexpected. We propose that excision from either the hippocamp al region or temporal neocortex may result in a disconnection, giving a similar functional outcome, as both types of resection interrupt a c ircuit likely to be essential for normal storage and retrieval of info rmation. (C) 1997 Elsevier Science Ltd.